Fossilized Pregnant Reptile Female Gives First Glimpse of Live Birth Over Egg Laying

A tantalising discovery of a near complete fossil of the marine reptile, Plesiosaur, has got scientists excited. The 78 million year old fossil is unique in the sense that this is the first time scientists have recovered a fully preserved skeleton, save the neck and skull. What more, this is a fossil of a pregnant female, complete with the baby within the womb. Possibly, the unfortunate creature got buried just before giving birth. This is the most crucial point Plesiosaur gave birth directly to young ones and did not lay eggs like so many of its reptile cousins. The fossil is on display at the National History Museum’s (NHM) Dinosaur Institute, Los Angelos County. (Yes, you can give it a visit).

The complete fossil (Courtesy: Dinosaur Institute, NHM, Los Angelos County)

The fossil and the animal

This startling fossil find answers the age-old question on the method of giving birth for Plesiosaur. The reptile was deemed too heavy and possessing hind limbs to weak to allow it to climb onto land and lay eggs. Neither were any Plesiosaur eggs or nests ever found. This find now seals that gap tight, establishing vivipary (or direct birth) amongst this important class of hunting lizards.

An artist's impression of a Plesiosaur

Plesiosaur lived about 78 million years ago, in the Mesozoic or the early Jurassic era. It was a large aquatic reptile, with flippers for swimming effortlessly and a slender neck and saw-like teeth. The skull structure, supported by the supple neck and the dentition, enabled it to be an effective hunter of fish. It was one of the top predators in the Western Interior Seaway, the large body of water, which used to split North America into two land masses, Larmidia and Appalachia.

Egg Laying vs Live Birth

This species of reptiles is among the very few that invests heavily in giving birth to one (or just a few) healthy offspring at a time, rather than laying eggs and investing in a large number of smaller and immature offsprings. Both evolutionary strategies exist and work successfully in the animal kingdom, but it is not known why a reptile should opt for vivipary over ovipary (egg-laying). Furthermore, vivipary involves caring for the young through the gestation period, requiring a complex social structure, which, in turn, involves individuals caring for each others’ babies.

Dr. F. Robin O’Keefe, who has been studying Plesiosaur fossils published a paper in the journal Science on the 12th of August on this find.


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Debjyoti Bardhan

Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.